Millionaire's Shortbread

This recipe is taken from "1001 Cupcakes, Cookies & other tempting treats" by Susanna Tee. We've been baking it for years now and every time the Twin visits me at Uni my house-mates put in an order for several boxes of these decadent treats. It's got to the point now that my house-mate's boyfriend magically appears at the house a few minutes after the Twin ever arrives, and a few minutes later he's already devoured about 3!
Note: although in the book it says makes 12 we've found it makes more like 20, depending on how big you want your shortbread.  We have also doubled the amounts for the shortbread base, otherwise the caramel can feel very thick in comparison.

Millionaire's Shortbread

Ingredients (Makes 12)

Shortbread:

• 230g butter
• 350g plain flour 
• 110g caster sugar 

Filling and topping:

• 175g butter
• 115g caster sugar 
• 3 tbsp golden syrup 
• 400g condensed milk 
• 200g plain chocolate/ dark cooking chocolate - the darker you can find the better! 

Method:

• Preheat the oven to 180 degrees Celsius. Line a square 9-inch baking tin with baking paper, using butter to stick it if necessary. 
• Sieve the flour then place along with the butter and sugar into a food processor and mix until everything is bound together and you have a smooth dough. Press the dough mixture into the tin and smooth the top. Bake in the oven for 20-25 minutes until golden brown.
• Remove and leave to cool. 
• Whilst the shortbread is cooling you can get started on the caramel filling. Place the butter, sugar, golden syrup and condensed milk into a saucepan and heat gently until the sugar has dissolved. Once the sugar is dissolved bring to the boil then reduce the heat and simmer for about 10 minutes, stirring the whole time. The mixture should become thick and a deep golden brown colour which indicates it is ready. If the mixture is still quite thin after 10 minutes of simmering keep stirring and simmering for another 5 minutes or so. 
• Pour over the shortbread base and chill in the fridge overnight. 
• To make the chocolate topping, break up the chocolate into chunks and place in a heatproof bowl over a pan of simmering water. Make sure the water in the pan is not too high- it should not touch the bowl at all. 2cm of water in the bottom of the pan will be sufficient. Stir the chocolate as it melts, taking the bowl off the pan and away from the heat when the chocolate is about 75% melted. Keep stirring and allow the heat of the chocolate to melt the remaining chunks. This technique should prevent the chocolate from burning.
• Allow to cool for a couple of minutes then spread over the caramel, then chill for a few hours. 
• Remove the millionaire's shortbread from the tin and cut into chunks.